I have a project where one Compute module (CM3) gets connected to two LAN9514 chips for Ethernet connectivity.
It seems that the raspberry pi uses the last 3 bytes of its serial number for the MAC on the LAN chips. That's all nice if you have one of them, but I'd say it is not allowed when there are two. Sure, when, as intended, the two interfaces end up on different networks, then there is no issue, but I'd think odd things would happen if they did get connected to the same network.
Shouldn't the ethernet driver think of a new MAC address to use? I've had 4-port ethernet cards in the past with just one EEPROM. The driver would then use the +1 +2 and +3 mac addresses on the other ports. In this case, that strategy might not be ideal: if serial numbers are assigned sequentially, when this goes into production and we buy 100+ CM3's in one go, it suddenly becomes likely that we'll end up with sequential serial numbers. Another pi with serial+1 on the same network would then cause an even bigger mess.
My proposal is to flip the "bit 23" in the MAC for the second LAN9514 chip.